[Marat Tanalin:]
>
>
> AFAICT, the "rule inside rule" change will be needed for CSS Hierarchies
> [1] anyway, so this should not be a problem.
>
That it would be needed for some other module not currently under active
discussion does not prove it would not be a larger change to the grammar.
And the existence of CSS Hierarchies does not prove there are no problems
with this pattern either.